Péter Fodor

Validation and uncertainty study of a comprehensive list of 160 pesticide residues in multi-class vegetables by liquid chromatography–tandem mass spectrometry

A rapid and sensitive liquid chromatography-tandem mass spectrometry method, in electrospray ionization positive mode, has been developed for the determination of 160 selected multi-class pesticides over a 33-min run time. Extracts were obtained using the acetonitrile-based QuEChERS (quick, easy, cheap, effective, rugged and safe) sample preparation technique. The validation study was carried out on tomato, pear and orange matrices following DG SANCO/2007/3131 of the European Quality Control Guidelines. These matrices represent high water, high sugar and high acidic content commodities, respectively. Matrix influence on recoveries and its effects on ionization were evaluated for the three matrices. Ten out of the 160 pesticides showed very low intensity, linearity and/or sensitivity problems. Linearity was studied in the 5-500 microg kg(-1) concentration range. Soft (<20%), medium (20-50%), and strong (>50%) matrix effects were obtained for 69%, 20%, and 11% of the studied compounds, respectively. Recoveries were investigated at the 10 and 100 microg kg(-1) levels, and depending on the commodity, 97%, 98% and 97% of the compounds in tomato, pear and orange, respectively, were in the 70-120% range. More than 90% of the investigated compounds had less or equal to a 5 microg kg(-1) limit of detection in the studied matrices. The relative standard deviations obtained exceeded 20% in only very few cases. The overall standard deviation obtained in the survey study (0.1551) was used for the methods uncertainty estimation. The expanded uncertainty resulted as being 0.3002 (coverage factor K=2, confidence level 95%). The method was applied on 59 real samples from 14 different kinds of fruits and vegetables. Thirty-three compounds were detected in 50 positive samples.

Arsenic speciation in freshwater organisms from the river Danube in Hungary

Total arsenic and arsenic species were determined in a range of freshwater samples (sediment, water, algae, plants, sponge, mussels, frog and fish species), collected in June 2004 from the river Danube in Hungary. Total arsenic concentrations were measured by ICPMS and arsenic species were measured in aqueous extracts of the samples by ion-exchange HPLC-ICPMS. In order to separately determine the efficiency of the extraction method and the column recovery, total arsenic concentrations in the extracts were obtained in three ways: (i) ICPMS determination after acid digestion; (ii) flow injection analysis performed directly on the extract; (iii) the sum of arsenic species eluting from the HPLC column. Extraction efficiencies were low (range 10-64%, mean 36%), but column recovery was acceptable (generally >80%) except for the fish samples, where substantial, currently unexplained, losses were observed. The dominating arsenic species in the extracts of freshwater algae were arsenosugars, whereas arsenate [As(V)] was present only as a minor constituent. On the other hand, plant extracts contained only inorganic arsenic, except for two samples which contained trace amounts of dimethylarsinate (DMA) and the tetramethylarsonium cation (TETRA). The oxo-arsenosugar-phosphate (ca. 35% of extractable arsenic) and the oxo-arsenosugar-glycerol (ca. 20%) as well as their thio-analogues (1-10%) were found in the mussel extracts, while arsenobetaine (AB) was present as a minor species only. In general, fish extracts contained only traces of arsenobetaine, and the oxo-arsenosugar-phosphate was the major arsenic compound. In addition, samples of white bream contained thio-arsenosugar-phosphate; this is the first report of a thio-arsenical in a fish sample. The frog presented an interesting arsenic speciation pattern because in addition to the major species, arsenite [As(III)] (30%) and the tetramethylarsonium cation (35%), all three intermediate methylation products, methylarsonate (MA), dimethylarsinate and trimethylarsine oxide (TMAO), and arsenate were also present. Collectively, the data indicate that arsenobetaine, the major arsenical in marine animals, is virtually absent in the freshwater animals investigated, and this represents the major difference in arsenic speciation between the two groups of organisms.

Routine approach to qualitatively screening 300 pesticides and quantification of those frequently detected in fruit and vegetables using liquid chromatography tandem mass spectrometry (LC-MS/MS)

This paper describes an efficient and effective analytical scheme to first screen for 300 pesticides in fruit and vegetables samples using liquid chromatography tandem mass spectrometry (LC-MS/MS) with a commercially enhanced product ion method. Then presumed positive extracts are analysed using a quantitative and confirmatory LC-MS/MS method optimized for 55 pesticides. A quick, easy, cheap, effective, rugged, and safe (QuEChERS) method with acetate buffering (AOAC Official Method 2007.01) was used for sample preparation, which has been previously shown to yield high-quality results for hundreds of pesticide residues in foods. The advantages and disadvantages of both the qualitative screening and quantitative/confirmatory methods and their combination are critically discussed. No false-negatives for the 55 pesticides occurred above 10 ng g−1 for extracts analysed by both LC-MS/MS methods, and the no false-positives were encountered from the screening analysis (after analyst review) because all presumptive identifications were confirmed in the second analysis. The monitoring scheme was applied during a one-year period on 200 fruit and vegetable samples from Hungarian markets. No pesticide residues were found in half the samples, and twelve violations of European maximum residue limits were detected.

Simultaneous speciation of redox species of arsenic and selenium using an anion-exchange microbore column coupled with a micro-concentric nebulizer and an inductively coupled plasma mass spectrometer as detector

Speciation methods for trace metals in the environment need rapid and accurate analyses. The simultaneous determination of redox species of arsenic (AsIII and AsV) and selenium (SeIV and SeVI) has been carried out by coupling a microbore column with a micro-concentric nebulizer (MCN) and inductively coupled plasma mass spectrometry (ICP-MS). The MCN, with its ability to nebulize liquids at low flow rates, was adapted to a small bore (2 mm id) microbore anion-exchange column. After optimizing the parameters of the MCN by factorial experimental design, an evaluation of the separation of redox As and Se species was carried out. The method was applied to the determination of the four species in a sample recommended for Se speciation studies, in a spiked natural water and in polluted soil leachings. No interference of 40Ar35Cl on 75As was observed when natural water samples were analyzed. The method showed good accuracy and repeatability in addition to facile handling and development. A detection limit of 1 ng ml–1 was found for the arsenic species and 4 ng ml–1 for the selenium species.

Study of the effects of operational parameters on multiresidue pesticide analysis by LC-MS/MS

In this paper, the influence of several operational parameters on a well established multiresidue LC-MS/MS method has been studied in relation to the analysis of 150 pesticides commonly present in vegetable samples. The operational parameters investigated are: (i) the influence of different modifiers (0.1% formic acid; 5mM ammonium formiate; 5mM ammonium acetate in aqueous phase) - both on the retention time and on the analytical response of the studied compounds; (ii) the effect of the analytical columns temperature on the retention time and on the analytical response of the pesticides investigated; (iii) the effects of co-elution in mixture containing 150 pesticides and, additionally, (iv) the carrying out of a study about the common transitions obtained by LC-MS/MS. Various common transitions were found among the 150 pesticides, but there were only two problematic cases, the pairs diuron-fluometuron and prometryn-terbutryn, which have common scanned transitions and have very close retention times. The use of ammonium salts as modifier instead of formic acid reports enhancement or suppression of the response depending on the pesticides. No great influence on the retention time or on the response of the pesticides and commodities studied was observed with relation to the column temperature. Two different columns: an HPLC (5 μm particle size) and an UHPLC analytical column (1.8 μm particle size) have been used. As was expected, shorter run times and lower peak width was achieved with the UHPLC column. In this paper, the effect of the compounds on each other in the MS analysis when the number of co-eluting compounds is quite high is also described. Mainly small suppression or enhancement co-elution effect was observed, but some particular pesticides presented high sensitivity (> ± 60% effect) when they elute together with others. This is an important factor and it has to be taken into account when performing multiresidue pesticide analysis.

Determination of arsenic species by high-performance liquid chromatography-ultrasonic nebulization-atomic fluorescence spectrometry

A novel technique involving the coupling of high-performance liquid chromatography with atomic fluorescence spectrometry using ultrasonic nebulization as an interface was assessed for the determination of AsIII, AsV, dimethylarsinic and monomethylarsonic acid. The effects of hydrogen and argon gas flow rates, nebulization temperature, loop volume, pump rate and phosphate buffer conditions on signal intensities were investigated. The detection limit for AsIII, AsV, DMAs and MMAs were 35, 50, 20 and 20 ng, respectively (for 250 mm3 volume injected). Linearity ranges were 250–2500 ng for all four arsenic species.

Determination of total mercury in sediments by microwave-assisted digestion-flow injection-inductively coupled plasma mass spectrometry

A method for the determination of total mercury in sediment samples was developed. Extraction of mercury from a sample matrix was carried out in an open vessel microwave digestion system while maintaining mild conditions during digestion in order to avoid any loss of mercury due to volatilization. A complexing agent (EDTA) and a surfactant (Triton X-100) were added to the samples in order to eliminate memory effects associated with mercury determinations and to obtain reproducible linear calibration curves. Standard additions and internal standardization were used for calibration and correction in an FI–ICP-MS detection system. The method was validated using the certified reference material PACS-1 and the reference materials IAEA-356 and S19 and gave results in good agreement with the certified and reference values. Sediment samples from Arcachon Bay were also analysed. Detection limits of 10 ng g -1 for solution and 1 ng g -1 for dry sediment samples were obtained.

Retrospective screening of relevant pesticide metabolites in food using liquid chromatography high resolution mass spectrometry and accurate-mass databases of parent molecules and diagnostic fragment ions

In recent years, the detection and characterization of relevant pesticide metabolites in food is an important task in order to evaluate their formation, kinetics, stability, and toxicity. In this article, a methodology for the systematic screening of pesticides and their main metabolites in fruit and vegetable samples is described, using LC-HRMS and accurate-mass database search of parent compounds and their diagnostic fragment ions. The approach is based on (i) search for parent pesticide molecules; (ii) search for their metabolites in the positive samples, assuming common fragmentation pathways between the metabolites and parent pesticide molecules; and (iii) search for pesticide conjugates using the data from both parent species and diagnostic fragment ions. An accurate-mass database was constructed consisting of 1396 compounds (850 parent compounds, 447 fragment ions and 99 metabolites). The screening process was performed by the software in an automated fashion. The proposed methodology was evaluated with 29 incurred samples and the output obtained was compared to standard pesticide testing methods (targeted LC-MS/MS). Examples on the application of the proposed approach are shown, including the detection of several pesticide glycosides derivatives, which were found with significantly relevant intensities. Glucose-conjugated forms of parent compounds (e.g., fenhexamid-O-glucoside) and those of metabolites (e.g., despropyl-iprodione-N-glycoside) were detected. Facing the lack of standards for glycosylated pesticides, the study was completed with the synthesis of fenhexamid-O-glucoside for quantification purposes. In some cases the pesticide derivatives were found in a relatively high ratio, drawing the attention to these kinds of metabolites and showing that they should not be neglected in multi-residue methods. The global coverage obtained on the 29 analyzed samples showed the usefulness and benefits of the proposed approach and highlights the practical benefit obtained when the so-called screening methods are used as a complementary tool to standard targeted LC-MS/MS methods.

Bioavailability of selenium from selenium-enriched green onions (Allium fistulosum) and chives (Allium schoenoprasum) after ‘in vitro’ gastrointestinal digestion

Three sample preparation methods—proteolysis to determine the initial species distribution, and an in vitro gastric and gastrointestinal digestion to assess the bioavailability of selenium—were applied to extract the selenium from selenized green onion and chive samples. Ion exchange chromatography was coupled to a high-performance liquid chromatography–ICP-MS system to analyze the selenium species of Allium samples. The difference in the selenium accumulation capability of green onions and chives was significant. Chive accumulated a one order of magnitude higher amount of selenium than did green onion. After proteolysis of both types of Allium plants, high amounts of organic selenium species such as MeSeCys, SeCys2 and SeMet became accessible. In the case of Se(VI)-enrichment, selenate was the main species in the proteolytic extract. After simulating the human digestion, the organic species were just slightly bioavailable compared with the results from proteolysis. The inorganic selenium content of the selenized samples increased significantly and SeOMet could be detected from the extracts. As an effect of the significant pH change between the gastric and the intestinal tracts, two oxidation processes took place: selenite oxidized to selenate, while SeMet oxidized to SeOMet.

High-performance liquid chromatography-hydride generation-atomic fluorescence spectroscopic determination of arsenic species in water

Abstract A method was developed for the determination of arsenite (AsIII), monomethylarsonate (MMAs), dimethylarsinate (DMAs), arsenate (AsV) from waters by using ion-pair chromatography hydride generation and atomic fluorescence spectrometry. A C18 bonded silica column modified by didoctyldimethylammonium bromide (DDAB) was used for separation. The effect of phosphate and methanol content of the eluent on the separation was investigated. The influence of five metals on hydride generation efficiency was tested. The optimal hydrogen chloride and sodium borohydride quantity for hydride generation was determined. The detection limit of the developed method, by using a 250-mm3 loop, was 0.4 ng/cm3 for AsIII, 0.8 ng/cm3 for DMAs, 0.6 ng/cm3 for MMAs and 1.2 ng/cm3 for AsV. The responses for all species tested were linear in 10–3000 ng/cm3 range.